1. Field of the Invention
The present invention relates to amplifier circuits and, in particular, is directed to a method and system for balancing a signal through parallel combined amplifier elements or amplifier sub-units within an amplifier device.
2. Description of the Related Art
RF power amplifiers are often configured as a plurality of amplifier elements that are combined in parallel. One example of the an RF power amplifier having parallel combined amplifier elements is a Base Transceiver Station (BTS) power amplifier. To implement the parallel configuration, the amplifier uses a power divider to divide the input signal between two or more parallel amplifier elements. The divided signal is amplified through the amplifier elements and then combined using a power combiner.
The various components of the amplifier may be subject to operational inconsistencies or defects. For example, the impedance of the amplifier elements, which are intended to be identical, may actually vary from one amplifier element to another in response to different input signal frequencies, input power levels, ambient temperatures, etc. Differences in gain and efficiency of different amplifier elements, variations in impedance matching components, imbalance in dividing power in the power divider, and variations in bias circuitry may also occur. These and other problems may cause an imbalance in the signals through the amplifier elements.
The effect of signal imbalances between amplifier elements is that one or more of the amplifier elements may operate in a more non-linear region than the other amplifier elements. This degrades the linearity of the overall amplifier and the reliability of the amplifier element which is under the heaviest stress, i.e., having the highest power consumption. Since some sub-units will no longer operate in an optimal region, the various sub-units may be driven at different power levels which degrades the overall efficiency and amplification characteristic of the amplifier device as a whole. Moreover, many of these problems become exacerbated when the amplifier operates at high power levels.
Different solutions to balance the signal between the various amplifier elements within an amplifier device are possible. Trimmer elements may be used to manually tune the operating conditions of the amplifier. Alternatively, larger and more expensive amplifier elements can be used to ensure linear performance and reliability in view of design margins for signal imbalance. High accuracy dividing and combining elements may also be used. However, these alternatives are relatively expensive and/or require user interaction.
The present invention is directed to a method and system to balance a signal through parallel combined amplifier elements or amplifier sub-units in an amplifier device. In one embodiment, automated adaptive feedback control is used to adjust an input parameter associated with one or more of the amplifier elements. Examples of the input parameters that may be adjusted include power level, impedance, and bias point.
A signal passing through each of the parallel amplifier elements is measured and compared. If a difference between the measured signals exceeds a predetermined threshold difference, an adjustment is then made by a control circuit to a pre-selected input parameter for at least one of the amplifier elements. As a result, each of the amplifier elements within the amplifier device are controlled to operate at their most efficient and reliable amplification range.
The present invention is that it allows for the automatic, fast, adaptive and continuous balancing of signals through the parallel combined amplifier elements, resulting in improved stability of the amplifier elements and overall improved performance, linearity, reliability, and efficiency of the entire amplifier device. The increased stability of the amplifier device also enables the use of cheaper components. Because the performance of each of the plurality of parallel amplifier elements in continuously monitored and controlled, cheaper, more optimal sized, and less tolerance matched amplifier elements can be used.
The amplifier device of the present invention is suitable for use as an RF power amplifier, such as an EDGE (Enhanced Data Rates for Global Evolution) power amplifier in a base transceiver station (BTS) having a balanced final stage. However, the amplifier-of the present invention is not limited to amplifiers operating in RF.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are intended solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims.